In general, dialysis apparatus used for the hemodialysis treatment is provided with a dialysate introducing line and a dialysate discharging line, respectively, to supply the dialyzer, connected to the blood circuit, with dialysate and discharge dialysate containing blood waste materials produced by dialysis. The tips of the dialysate introducing line and the dialysate discharging line are connected, respectively, to a dialysate introducing port and a dialysate discharging port of the dialyzer.
In a blood purification instrument (dialyzer) applied to a hemodialysis filter (HDF) and using dialysate as the infusion solution (hereinafter referred to as “online HDF”), it is necessary to infuse the dialysate into the blood of a patient by an amount of ultrafiltration. Accordingly, a dialysis apparatus is proposed, for example in Japanese Laid-open Patent Publication No. 313522/2004. As shown, the dialysis apparatus has a blood circuit with a dialyzer 101 including an arterial blood circuit 102, arranged with a blood pump 104, and a venous blood circuit 103. A dialysate introducing line L1 introduce the dialysate, supplied by a pump 105, into the dialyzer 101. A dialysate discharging line L2 discharges the dialysate from the dialyzer 101. A bypass line L4 connects the dialysate introducing line L1 and the dialysate discharging line L2, not via the dialyzer 101. A dialysate infusing line L3 is coupled between the bypass line L4 and arterial blood circuit 102.
Such a dialysis apparatus of the online HDF is structured so that it ultrafiltrates a predetermined amount of water from blood during the hemodialysis treatment. It then replaces the ultrafiltrated water with dialysate while supplying the dialysate from the dialysate infusing line L3. A dialysate infusing pump 106 controls the flow rate through the dialysate infusing line L3 during the dialysate infusion. In FIG. 6, reference numerals 109 and 110 denote filters for filtering dialysate flowing through the dialysate introducing line L1. Reference character “V” denotes an electromagnetic valve. In addition, air trap chambers D1, D2 are arranged, respectively, on the arterial blood circuit 102 and the venous blood circuit 103.
The dialysis treatment is performed by connecting the base end of the dialysate infusing line L3 to one T-tube 107. The other tip end of the dialysate infusing line L3 is connected to the tip end of a tube “c” that extends from the air trap chamber D1 of the arterial blood circuit 102. The dialysate is infused from the air trap chamber D1 by an amount of water to be filtered (pre-dialysate infusion). The dialysate infusion (post-dialysate infusion) can also be performed by connecting the tip end of the dialysate infusing line L3 to the tip end of a tube extended from the air trap chamber D2.
The blood-return, after the dialysis treatment, can be performed by a dialysis apparatus as shown in FIG. 7. The tip end of the dialysate infusing line L3 is connected to the tip end (similarly to the priming, a connector after removal of an arterial puncture needle) of the arterial blood circuit 102. The dialysate is supplied from the pump 105 while keeping a puncture needle at the tip end of the venous blood circuit 103 punctured into a patient. This enables blood remaining in the blood circuits to be replaced with dialysate and the remaining blood to be returned into the body of a patient from the venous puncture needle. During this blood-returning process, it is also necessary to drive both the dialysate infusing pump 106 and the blood pump 104 to the normal rotational direction.
However, problems exist in the dialysis apparatus of the prior art. Usually, there is an error in the flow rate caused by general purpose pumps such as blood pump and dialysis pump relative to the set flow rate (discharging amount). Accordingly, it is believed that an excessive positive pressure would be caused in a flow route between the blood pump 104 and the dialysate infusing pump 106. Thus, the flow route would be broken when, for example, the discharging amount of the blood pump 104 is lower than that of the dialysate infusing pump 106 in the blood-returning process if the blood pump 104 is connected in series as shown in FIG. 7.